四川盆地中部蓬莱地区灯二段沉积微相演化及气藏综合评价

Sedimentary microfacies evolution and comprehensive evaluation of gas reservoir of the Dengying Member 2 in Penglai area,central Sichuan Basin

PT1井区灯二段的重大突破及集中评价成果证实了四川盆地川中古隆起北部斜坡区灯二段发育台缘优质孔洞型储层而且具备优越的岩性气藏条件。为进一步描述蓬莱地区丘滩体岩性气藏特征并评价其勘探潜力,综合利用钻录井、测井、地震等资料,对PT1井区灯二段微相特征及沉积演化过程进行研究分析。结果表明:①灯二段发育典型台缘高能丘滩沉积,岩性以凝块白云岩、泥粉晶白云岩为主,可识别出丘核、丘坪、丘间等微相类型,具有多种相序组合特征;②基于碳同位素、电阻率曲线及井震标定结果可将灯二段分为3个小层,各小层纵、横向上厚度及微相具有不同程度的分异特征;③通过小层时间厚度、内部振幅能量与微相发育的相关性分析,明确了早、中、晚三期沉积微相平面展布特征,并建立了PT1井区灯二段沉积演化模式;④在构造形态及统一气水界面的控制下,PT1井区灯二段主体气藏集中分布在灯二-3小层,内部受沉积微相约束具有一定分异性。对该岩性气藏进行多因素综合评价,划分出三大类有利勘探区。

The great breakthrough and centralized evaluation results of the second member of Dengying Formation(Dengying Member 2)in PT1 Well Block confirmed the development of high-quality marginal platform porous-vuggy reservoir and the favorable conditions of lithologic gas reservoir in the northern slope zone of central Sichuan paleouplift.In order to further describe the characteristics of the mound-shoal lithologic gas reservoir in Penglai area and evaluate its exploration potential,this paper analyzes the microfacies characteristics and sedimentary evolution process of the Dengying Member 2 in PT1 Well Block by making comprehensive use of drilling,logging and seismic data.The results show that:(1)High-energy mound-shoal deposit of typical marginal platform is developed in the Dengying Member 2,the lithology is dominated by clotted dolomite and micrite-very finely crystal dolomite,and mound core,mound flat and inter-mound microfacies can be identified,presenting the characteristics of multiple facies sequence combination.(2)Based on carbon isotope,resistivity curve and well-seismic calibration results,the Dengying Member 2 can be divided into three submember,the thickness and microfacies of which presents the differential characteristics of different degrees in vertical and lateral.(3)Based on the correlation between the microfacies and time thickness and internal amplitude energy of submember,the distribution characteristics of sedimentary microfacies in three stages(early,middle and late)are clarified and the sedimentary evolution model of the Dengying Member 2 in PT1 Well Block is established.(4)Under the control of structural morphology and uniform gas-water interface,the main gas reservoir of the Dengying Member 2 in PT1 Well Block is mainly distributed in submember 3 of Dengying Member 2 and is differential to some extent due to the constraint of sedimentary facies internally.Accordingly,this lithologic gas reservoir is evaluated comprehensively based on multiple factors and it is divided three types of exploration area,in which class I and II areas have large water avoidance and gas column height,and are the best dessert areas for the next concentrated exploration.This proposed evaluation method can further provide important support and reference for the subsequent exploration of lithologic gas reservoirs of Dengying Formation in the slope zone of central Sichuan paleouplift.